1. Field of the Invention
The invention relates to a fixed auger assembly for generating turbulent air flow in an exhaust air stream of a diesel engine.
2. Description of the Related Art
In combustion exhaust streams, urea, also known as carbamide, can be used as a nitrogen oxide (NO and N2O, which are together called NOx) reducing agent. For example, in diesel engines, urea is injected into the exhaust air stream to control NOX emissions. The injected urea decomposes to ammonia upon heating, which reacts with NOX across a catalyst located downstream of the injection point to reduce the amount of NOX in the exhaust air stream. The reaction produces water, nitrogen, and carbon dioxide (CO2), which are relatively harmless as air pollutants as compared with NOX. It is known to use a fixed auger to generate turbulent air flow and increase mixing between the urea and the exhaust air stream before exposure to the catalyst.
Prior art augers comprise a pair of auger blades welded to a shaft, which is then inserted into a tubular casing. Typically, the auger blades are fixed within the tubular casing by spot welding the edges of the auger blades to the inside of the tubular casing. Then, a reducer (a truncated cone section) is welded to each end of the tubular casing to enable coupling of the auger to the exhaust line. Extensive time and labor is required to assemble all of these components. Furthermore, the weld bead created by the spot welding process used to attach the edges of the auger blades to the inside of the tubular casing is exposed to the corrosive exhaust air stream containing urea, and can eventually fail.